1. Field of the Invention
The invention relates to a writing or drawing instrument with a housing, wherein a writing point is provided on the front, and, towards the rear, a writing fluid reservoir is provided in the housing interior. The reservoir is connected to ambient air via a capillary pressure equalization system.
2. Brief Description of the Prior Art
Writing and drawing instruments of this type typically are called tubular writing instruments. The writing point consists of a writing tube that is supplied with ink from an ink cartridge placed on a rear part of a housing which supports the writing tube. Pressure equalization is provided via a capillary pressure equalization chamber, one end of which is connected to the ambient air and the other to the interior of the housing containing ink. Hence, a partial vacuum, or underpressure, is not created in the ink reservoir when ink is expended, thus hampering a further output of ink by the writing tube. The pressure equalization chamber also receives ink if there should be overpressure in the ink reservoir. This factor is of particular importance in writing and drawing instruments of the type of interest here. An ink reservoir also contains air which expands, upon a rise in temperature, to a greater extent than the writing fluid so as to cause a considerable overpressure that will push a comparatively large amount of writing fluid into the pressure equalization chamber. As a result, writing fluid can exit through the end of the pressure equalization chamber connected to the ambient air, and lead to soiling.